Glossary of Aquifer Testing Terms

by Glenn M. Duffield, President, HydroSOLVE, Inc.

General

Aquiclude: A water-bearing layer of rock or sediment that is incapable of transmitting water.
Aquifer: A water-bearing layer of rock or sediment capable of transmitting significant quantities of water.
Aquifer Thickness (b): Saturated thickness of an aquifer. [L]
Aquitard: A water-bearing layer of rock or sediment that transmits small quantities of water in relation to aquifers.
Artesian Aquifer: A confined aquifer in which the water level in wells rises above the top of the aquifer.
Barrier Boundary: See no-flow boundary.
Confined Aquifer: An aquifer confined between aquitards or aquicludes. See also leaky confined aquifer and nonleaky confined aquifer.
Confining Unit: See aquiclude and aquitard.
Constant-Head Boundary: An aquifer boundary where no drawdown occurs.
Displacement (H): Change in water level (rise or fall) measured from static position. [L]
Drawdown: Change in water level due to an external stress such as pumping. [L]
Flowing Artesian Aquifer: A confined aquifer in which the water level in wells rises above ground surface.
Initial Displacement (H₀): Change in water level (rise or fall) measured from static position in the control well at start of a slug test. [L]
Leaky Confined Aquifer: A confined aquifer which has aquitards at its upper and/or lower boundaries.
Negative Boundary: See no-flow boundary.
No-Flow Boundary: An aquifer boundary across which no flow occurs.
Nonleaky Confined Aquifer: A confined aquifer which has aquicludes at its upper and lower boundaries.
Normalized Head (H/H₀): Displacement in a well divided by initial displacement. [dimensionless]
Phreatic Aquifer: See unconfined aquifer.
Positive Boundary: See constant-head boundary.
Recharge Boundary: See constant-head boundary.
Residual Drawdown: Drawdown during the recovery phase of a pumping test. [L]
Unconfined Aquifer: An aquifer which has a water table forming its upper boundary.
Water Table: The surface in a porous medium on which fluid pressure is equal to atmospheric pressure.
Water-Table Aquifer: See unconfined aquifer.

Hydraulic Properties

Aquifer Diffusivity (α): The ratio of transmissivity to storativity, α=T/S. [L²/T]
Coefficient of Storage: See storativity.
Hydraulic Conductivity (K): Constant of proportionality defining the specific discharge of a porous medium under a unit hydraulic gradient, q=K*i. [L/T]
Hydraulic Gradient (i): Hydraulic head loss per distance, i=dh/dl. [dimensionless]
Porosity (n): Ratio of void volume (V_v) to total volume (V_T) in a rock or unconsolidated material, n=V_v/V_T. [dimensionless]
Specific Discharge (q): Flow rate per unit cross-sectional area of aquifer, q=Q/A. Also known as Darcy velocity or Darcy flux given by the product of hydraulic conductivity and hydraulic gradient, q=K*i. [L/T]
Specific Storage (S_s): Volume of water released from storage from a unit volume of aquifer per unit decline in hydraulic head. [1/L]
Specific Yield (S_y): Volume of water released from storage by an unconfined aquifer per unit surface area of aquifer per unit decline of the water table. [dimensionless]
Storativity (S): Volume of water released from storage by a confined aquifer per unit surface area of aquifer per unit decline in hydraulic head normal to surface equal to product of specific storage and saturated thickness, S=S_sb. [dimensionless]
Storage Coefficient: See storativity.
Transmissivity (T): The product of hydraulic conductivity and saturated thickness, T=K*b. [L²/T]

Well Construction Details

Filter Pack: Material (typically sand or gravel) emplaced in well annulus around open interval of a well (e.g., well screen).
Full Penetration: A fully penetrating well has a perforated interval or screen extending over the full saturated thickness of an aquifer.
Gravel Pack: See filter pack.
Partial Penetration: A partially penetrating well has a perforated interval or screen extending over a portion of the saturated thickness of an aquifer.
Sand Pack: See filter pack.